Rack ovens are generally equipped with a fuel-fed heating element and a fan for moving heated air throughout a baking chamber to provide a rapid distribution of hot air over the food product. Commercial ovens of this type include a baking chamber, which is sized to receive a rack having multiple shelves containing products to be baked; a power driven, rotating mechanism to rotate the product as it is being cooked or baked; a heat exchanger including one or more gas burners and an exhaust system to eliminate combustion gases; and a circulating system for directing hot air along a heated air flow path that passes through the baking chamber. Conventional rack ovens of the type for baking bread also generally include a steam generator for the introduction of steam into the oven for brief periods of time, usually at the beginning of the baking process, to impart a desired appearance to the baked food product.
In convection ovens such as that described in U.S. Pat. No. 5,617,839, a rack oven includes a heat exchanger comprising a plurality of heat exchange tubes, and a plurality of gas fired in-shot burners, wherein each of the in-shot burners fires into a corresponding heat exchange tube. One or more blowers circulate air past the heat exchange tubes and to the oven baking chamber. The input openings of the plurality of heat exchange tubes are arranged in a plurality of horizontal rows, each row containing a plurality of input openings, the rows spaced vertically from each other. Each tube then extends across an air flow region into a vertical gas collection duct, with corresponding tubes then extending back across the air flow region to another gas collection duct and so on. It is also known to provide heat exchange tubes having appropriate bends. In either case, the air flow of the oven is generally upward across the heat exchange tubes, over the top of the baking chamber in a plenum, downward and into the baking chamber through distribution ports in a wall of the chamber, then out of the baking chamber and back upward through the heat exchanger.
FIGS. 7A and 7B illustrate another PRIOR ART rack oven construction 100 in which a heat exchanger section 102 is positioned alongside the baking chamber 104. The wall 106 separating the baking chamber 104 from the heat exchanger section 102 includes a single, centrally disposed opening 108 having an axial fan 109 positioned therein. The wall 106 also includes louvers 110 towards the sides thereof. The heat exchanger section 102 includes a plurality of horizontally extending, U-shaped exchange tubes 112, with tube segments 120 and 122, are arranged vertically one above the other. When the fan 109 is rotated, air flows from the baking chamber 104, through the opening 108 onto a central section of the heat exchange tubes and then splits in two lateral directions along the heat exchange tubes to be returned to the baking chamber via louvers 110 as best seen by the arrows in FIG. 7A. As best reflected in FIG. 7B, there is also a substantial vertical (upward and downward) component to the air flow in the heat exchanger section 102 due the central location of the opening 108. Likewise, there would be a significant vertical component to the air flow in the baking chamber 104 as well. A steam generator (not shown) is also provided in the prior art oven 100. As best seen in FIG. 7C, the U-shaped heat exchange tubes 112 are arranged at progressively increasing angles to the horizontal when moving away (either upward or downward) from a vertically central location 124 of the tubes.